1. Field of the Invention
This invention relates to an image processing apparatus incorporated in a camera using silver salt film, a video camera or the like, and provided with a visual axis detecting device including an area sensor (CCD) for detecting a photographer's eyeball and an area sensor for converting an incident image into an electrical signal.
2. Related Background Art
In recent years, there has been proposed a visual axis detecting device by which, in order to detect a photographer's visual axis, the photographer's eyeball is illuminated by an infrared light emitting diode (hereinafter referred to as the IRED) and the angle of rotation in a direction in which the eyeball is seeing is calculated from the position of a reflected image on the cornea of the eyeball by the IRED (which reflected image is called Purkinje's image) and the position of the center of the pupil found from the boundary (edge, which is a characteristic point) between the infrared-illuminated iris and the pupil, whereby at what position on the finder image of a camera the photographer is looking, is discriminated. Such a detecting device is proposed in U.S. application Ser. No. 07/888,495.
As a device of this kind, there is known, for example, one in which it is incorporated in a single-lens reflex camera provided with an auto focus device and the distance measuring point of the auto focus device is selected on the basis of visual axis information from the visual axis detecting device and auto focusing is effected at that distance measuring point.
In the above-described example of the prior art, however, what type of area sensor is best suited as an area sensor for obtaining eyeball image data has been unknown.
As the type of CCD (charge coupled device) area sensor popular in video cameras and the like, use has heretofore been made of a CCD of the interline (hereinafter referred to as IT) type. A conceptional view of the IT type CCD as it is seen from a surface near a certain picture element on the sensor chip surface thereof is designed as follows.
FIG. 9 of the accompanying drawings shows four picture elements picked out, and hatched portions are opening portions, i.e., areas A in which light reception is effected, and neighboring portions B are the areas of a CCD for vertical transfer.
Charges received and accumulated in the areas A (light receiving portions) are shifted to the areas B (CCD portions for vertical transfer) immediately adjacent to the areas A by operation of an electrode generally called a shift electrode, and are downwardly vertically transferred in conformity with the reading-out of a CCD image signal.
In this way, the light receiving portions and the CCD portions for vertical transfer are two-dimensionally disposed and, therefore, the numerical aperture of the light receiving portion in a picture element becomes small, and generally is a value of about 30%. Therefore, the corneal reflected image of the IRED, i.e., Purkinje's image, becomes considerably small on the area sensor and thus, comes into an insensitive zone on the area sensor, and this gives rise to a problem that the Purkinje's image cannot be detected.
Accordingly, an area sensor of great numerical aperture is desirable as the area sensor in the above-described visual axis detecting device.
Also, as a countermeasure for the saturation of the light receiving portions in the above-described IT type CCD, vertical type overflow drain structure for permitting overflowed charges to escape to a substrate so as not to come into the CCD portions for vertical transfer and the picture elements adjacent thereto is adopted. However, due to this vertical type overflow drain structure, rays of long wavelength light like infrared light which arrive at even the deep portion of the substrate are not effectively utilized, and this leads to a problem that sensitivity to infrared light is reduced.
Further, generally in a method of introducing eyeball data in a visual axis detecting device, control is effected for an area sensor in the flow of accumulation, reading-out and processing. In this case, an inexpensive A/D converter takes much A/D conversion time and thus, control is effected with a time distribution of about several ms for accumulation and several hundreds of ms for reading-out, and the reading-out time is much longer than the accumulation time.
When the use of the IT type CCD is considered at such a time, the reading-out rate is slow after the charges are shifted to the CCD portions for vertical transfer after the termination of accumulation and therefore, the leakage of light from the light receiving portions into the CCD portions for vertical transfer occurs. This is called smear, and the amount of this cannot be neglected, and this leads to a problem that image data are deteriorated.
Also, an area sensor having high sensitivity to infrared light is desirable as the area sensor in the above-described visual axis detecting device, because it is necessary to effect detection by the use of infrared illumination without making the photographer conscious of the illumination.